Everything above -10°C is no problem at all for storage. But it is important to fully switch it off and not use it as long as the battery temp low.
Storing in the cold is better than storing in the warm. The chemical reactions and therefore aging of the battery are slowed down. But don't use the bike when the battery is cold.
50% SOC is ideal for storage. Don't let it sit below 20% or above 80%. High and low SOCs will speed up the aging of the battery. If the SOC drops below 0%, the battery could even be damaged. Very important: Don't charge when the battery temp is low (I would not charge it when below 5°C).
So when storing over winter, charge it to about 60%, fully shut it down and put it in a place not too cold.
I've always shot for 50% - 60% SOC with all of my lithium batteries that I store off season (everything from Surron batteries, eMTB, camper batteries, fishing boat trolling motor batteries, etc.). I have an uninsulated and unheated shop, though, so it gets cold. Heck, winter has barely started and it was 15F / -9C this morning. -10F / -23C is just a normal winter day and we usually get a week here and there where F and C "go to meet". Ha. (-40F/-40C is where F and C meet). I keep my little pop-up pickup camper at about 32F/0C inside and so set most of my lithium batteries in there that I'm storing for the winter. I don't charge the ones I store over the winter, but most of my larger lithium have internal heating if I needed to do so. Plus, they all have cold disconnect sensors in BMS if they were too cold, the BMS wouldn't allow charging anyway. I have some that are in the cold shop because I use them all winter, but again, they have internal heaters so the BMS directs current to internal heating elements until the cell temps are plenty warm and only then redirects the current to charge the cells.
The Varg really complicates this situation. It can't fit in my little camper, of course, and too much of a pain to remove the battery. I did buy a electric battery surround that hangs on it. Draws about 34watts so a couple bucks a month. Doesn't fit snug because of frame and skid plate, but will hopefully make a little micro climate around the battery to at least take the edge off. Most people that live in cold climates don't have an option but to leave things in the cold so we do what we can. I'd lean it against the wall in the living room if it was up to me, but so far the "there is no gas/oil/exhaust smell" argument has not swayed my wife. Ha.
I assume the Varg has a BMS that doesn't allow charging in the cold. Anyone plug in the charger below freezing and see if it pops a message?
I worry a bit about the cold, but I worry more about the heat with all my batteries. Summer time in the uninsulated shop is usually hotter than outside temps (80 - 90F and a dozen days hit 100F in there). Luckily, things cool off quickly at night here and so the shop is usually only at those temps for a few hours in the height of the afternoon heat. Overnight, it cools down into the 60s.
In the end, I'll do what I can if it's convenient, but they are pretty much either going to last or not. Not a lot more I can do, especially with the Varg since I'm not removing the battery for the winter much less during the riding season.
